Pickup cartridge with moving magnet armature

Abstract

A pickup cartridge of the moving magnet type. The vibration center of its vibrating system is stabilized by being concentrated at a certain point without appreciable fluctuations, regardless of the vibration amplitude of the vibrating system. Also, it has a very high conversion efficiency of its displacement-magnetism converting system for converting the positional changes of this vibrating system to changes in magnetism. This conversion efficiency is almost constant regardless of the vibration amplitude of the vibrating system. A damping member is interposed between an armature magnet and a member for supporting this armature magnet. A cantilever attached to the magnet is pulled, jointly with the armature magnet, by a tension wire connected to the base of this cantilever, toward the supporting member in the axial direction of the cantilever. The base end of the cantilever is positioned substantially at the center of that surface of the armature magnet which faces the supporting member via the damping member. The other surface of the armature magnet faced by the pole pieces of the displacement-magnetism converting system is a plane having a substantially constant radius of curvature centering around the base of the cantilever.

I claim: 
     
       1. A pickup cartridge comprising: an armature formed as a permanent magnet;   a supporting member for supporting said armature magnet;   a damping member made with an elastic material for damping the movement of said armature magnet and positioned between said supporting member and a first surface of said armature magnet, which first surface facing said damping member;   a cantilever secured to said armature magnet and having its foremost end provided with a stylus tip and having its base end positioned at substantially the center of said first surface of the armature magnet;   position insuring means for insuring the position of the base end of said cantilever relative to said supporting member and permitting the free movement of said cantilever centering around said base end thereof;   pole pieces facing a second surface of said armature magnet at positions close to this second surface and arranged symmetrically with respect to said cantilever so that an area of each of said pole pieces facing said second surface of the armature magnet is constant irrespective of vibration of the armature magnet, which second surface does not face said damping members;   a yoke magnetically coupled to said pole pieces for constituting a closed magnetic path for the passage of the magnetic flux emitting from said armature magnet, said yoke being arranged at a specific position relative to said supporting member; and   a coil applied around said yoke for inducing a signal corresponding to the variation of the magnetic flux passing through said yoke,   said second surface of the armature magnet being a surface having a substantially constant radius of curvature centering around the base end of said cantilever,   said pole pieces pointing to the base end of said cantilever and having end faces thereof facing said second surface of the armature magnet at postions close to this second surface.   
     
     
       2. A pickup cartridge according to claim 1, in which: said position insuring means in a suspension wire for pulling said cantilever jointly with said armature magnet substantially in the axial direction of this cantilever toward said supporting member.   
     
     
       3. A pickup cartridge according to claim 2, in which: said suspension wire is made with a flexible material having a small elongability and having one end coupled to the base end of said cantilever and the other end fixed to said supporting member.   
     
     
       4. A pickup cartridge according to claim 1, in which: said first surface of the armature magnet represents a flat surface facing substantially parallel to said supporting member, and   said second surface of the armature magnet represents a spherical surface centering around the base end of said cantilever.   
     
     
       5. A pickup cartridge according to claim 1, in which: said yoke is of a substantially U-shape, and   said pole pieces are formed integrally with said yoke by bending the two end portions of said yoke substantially toward the base end of said cantilever.   
     
     
       6. A pickup cartridge according to claim 1, in which: said first surface of the armature magnet represents a surface projecting progressively toward said supporting member as it goes from its marginal edge portion toward its center, and   said damping member has a thickness progressively increasing as it goes from its center portion toward its marginal edge portion.   
     
     
       7. A pickup cartridge according to claim 1, in which: that surface of said supporting member which faces said first surface of the armature magnet is formed into a convex surface progressively projecting toward said armature magnet of this surface approaches close to the base end of said cantilever, and   said damping member has a thickness progressively increasing as it goes from its center toward its marginal edge portion.   
     
     
       8. A pickup cartridge according to claim 7, in which: said convex surface of the supporting member represents a conical surface having its apex located at its portion facing the base end of said cantilever, and   said damping member has a conical surface having its apex located at its center and being concave in shape extending in the direction departing farther from said supporting member.   
     
     
       9. A pickup cartridge according to claim 1, in which: said first surface of the armature magnet represents a surface projecting progressively toward said supporting member as it goes from its marginal edge portion toward its center,   that surface of said supporting member which faces said second surface is formed into a convex surface projecting pregressively toward said armature magnet as it approaches closer to the base end of said cantilever,   said damping member has a thickness progressively increasing as it goes from its center toward its marginal edge portion.   
     
     
       10. A pickup cartridge according to claim 9, in which: said first surface of the armature magnet represents a conical surface having its apex located at its center,   said projecting surface of said supporting member represents a conical surface having its apex located at its portion facing said cantilever, and   the bilateral surfaces of said damping member are provided in the form of a concave conical surface having its apex located at its center.   
     
     
       11. A pickup cartridge according to claim 1, in which: said pole pieces are fixec to said supporting member, respectively, and they have magnetic coupling portions exposed on the side surfaces of said supporting member for magnetic coupling, and   said yoke is magnetically coupled to each of said pole pieces at said magnetic coupling portions of these pole pieces to thereby form said closed magnetic path.   
     
     
       12. A pickup cartridge according to claim 11, in which: said yoke has lug portions facing the side surfaces of said supporting member, and   the foremost ends of these lug portions engage said magnetic coupling portion of said pole pieces to thereby magnetically couple said yoke to said pole pieces.   
     
     
       13. A pickup cartridge according to claim 11, in which: said yoke has lug portions engaging the outer sides of said supporting member to magnetically couple said supporting member to said yoke, keeping the yoke at said specific position relative to said supporting member.   
     
     
       14. A pickup cartridge according to claim 13, in which: the respective one ends of said lug portions are coupled by a member made with a magnetic material,   said coil is applied around this member, and   under the state in which said yoke is magnetically coupled to said supporting member by said lug portions of the yoke with said specific positional relationship, said lug portions engage said magnetic coupling portion of said pole pieces to thereby couple said pole pieces to said yoke magnetically.   
     
     
       15. A pickup cartridge comprising: an armature formed as a permanent magnet;   a supporting member for supporting said armature magnet;   a damping member made with an elastic material for damping the movement of said armature magnet and positioned between said supporting member and a first surface of said armature magnet, which first surface facing said damping member;   a cantilever secured to said armature magnet and having its foremost end provided with a stylus tip and having its base end positioned at substantially the center of said first surface of the armature magnet;   position insuring means for insuring the position of the base end of said cantilever relative to said supporting member and permitting the free movement of said cantilever centering around said base end thereof;   pole pieces facing a second surface of said armature magnet at positions close to this second surface and arranged symmetrically with respect to said cantilever so that an area of each of said pole pieces facing said second surface of the armature magnet is constant irrespective of vibration of the armature magnet, which second surface does not face said damping member;   a yoke magnetically coupled to said pole pieces for constituting a closed magnetic path for the passage of the magnetic flux emitting from said armature magent, said yoke being arranged at a specific position relative to said supporting member; and   a coil applied around said yoke for inducing a signal corresponding to the variation of the magnetic flux passing through said yoke, said second surface of the armature magent representing a substantially conical surface using said cantilever as its center axis,   said pole pieces pointing to the base end of said cantilever and having said second surface of the armature magnet at positions close to this second surface.   
     
     
       16. A pickup cartridge comprising: an armature formed as a permanent magnet;   a supporting member for supporting said armature magnet;   a damping member made with an elastic material for damping the movement of said armature magnet and positioned between said supporting member and a first surface of said armature magnet; which first surface facing said damping member;   a cantilever secured to said armature magnet and having its foremost end provided with a stylus tip and having its base end positioned at substantially the center of said first surface of the armature magnet;   position insuring means for insuring the position of the base end of said cantilever relative to said supporting member and permitting the free movement of said cantilever centering around said base end thereof;   pole pieces facing a second surface of said armature magnet at positions close to this second surface and arranged symmetrically with repect to said cantilever, so that an area of each of said pole pieces facing said second surface of the armature magnet is constant irrespective of vibration of the armature magnet, which second surface does not face said damping member;   a yoke magnetically coupled to said pole pieces for constituting a closed magnetic path for the passage of the magnetic flux emitting from said armature magnet, said yoke being arranged at a specific position relative to said supporting member; and   a coil applied around said yoke for inducing a signal corresponding to the variation of the magnetic flux passing through said yoke,   said second surface of the armature magnet being a surface having a substantially constant radius of curvature centering around the base end of said cantilever,   in the rest position of that armature, the tip portions of the pole pieces face the second surface of the armature at a position in the vicinity of the intermediate portion between the front the rear ends of the armature.   
     
     
       17. A pickup cartridge comprising: an armature formed as a permanent magnet;   a supporting member for supporting said armature magnet;   a damping member made with an elastic material for damping the movement of said armature and positioned betweem said supporting member and a first surface of said armature magnet, which first surface facing said damping member.   a cantilever secured to said armature magnet and having its foremost end provided with a stylus tip and having its base end positioned at substantially the center of said first surface of the armature magnet;   position insuring means for insuring the position of the base end of said cantilever relative to said supporting member and permitting the free movement of said cantilever centering around said base end thereof;   pole pieces facing a second surface of said armature magnet at positions close to this second surface and arranged symmetrically with respect to said cantilever, so that an area of each of said pole pieces facing said second surface of the armature magnet is constant irrespective of vibration of the armature magnet, which second surface does not face said damping member;   a yoke magnetically coupled to said pole pieces for constituting a closed magnetic path for the passage of the magnetic flux emitting from said armature magnet, said yoke being arranged at a specific position relative to said supporting member; and   a coil applied around said yoke for inducing a signal corresponding to the variation of the magnetic flux passing through said yoke, said second surface of the armature magnet representing a substantially conical surface using said cantilever as its center axis and having its apex located at a position in the extension of the base end of said cantilever,   in the rest position of the armature, the tip portions of the pole pieces face the second surface of the armature at a position in the vicinity of the intermediate portion between the front and rear ends of the armature.